Variable voltage transformer



Oct. 12, 1965 w, KOBER 3,212,039

VARIABLE VOLTAGE TRANSFORMER Filed June 8, 1961 2 Sheets-Sheet 1INVENTOR.

BY William Kobar,

ATTORNEYS Oct. 12, 1965 w. KOBER 3,212,039

VARIABLE VOLTAGE TRANSFORMER Filed June 8. 1961 2 Sheets-Sheet 2 F194.FJ'Q5. FiQd INVENTOR. WJJZJam ffober,

ATTORNEYS. v

United States Patent Office 3,212,039 Patented Oct. 12, 1965 3,212,039VARIABLE VOLTAGE TRANSFORMER William Kober, Fairport, N.Y., assignor, bymesne assignments, to The Garrett Corporation, Los Angeles, Calif., acorporation of California Filed June 8, 1961, Ser. No. 115,669 15Claims. (Cl. 33677) This invention relates generally to the electricalcontrol art, and more particularly to a new and useful variable voltagetransformer.

Pending application Serial No. 695,394, filed November 8, 1957 in thename of Norbert N. Bojarski, and now abandoned in favor of continuationapplication Serial No. 179,881 filed February 8, 1962, now Patent No.3,154,766, issued Oct. 27, 1964, discloses a multipurpose transformerintended to produce an output voltage which can be varied smoothly andcontinuously in infinitesimal increments, and which does not requirebrushes or other current carrying moving parts. Such a transformer has amagnetic armature section movable relative to a primary and twosecondary legs to divert primary flux from one secondary leg to theother. This varies the secondary or output voltage which is intended tobe determined by the relative area of working contact between themovable armature and the respective secondary legs.

However, such a transformer construction poses certain problems which itis the primary object of this in- .vention to solve. These problemsarise from the fact that the division of primary flux between thesecondary legs is determined not only by the relative area of Workingcontact between the armature and the secondary end faces, but also bythe saturation level of the magnetic material. The flux is not constant,but varies approximately sinusoidally, whereby only at peak levels doesthe flux limitation by saturation act in a compelling manner. Atinstantaneous flux levels below the maximum, such as one-half themaximum, a restricted area of contact between the armature and an endface could pass twice the amount of flux needed. As the instantaneousflux level rises, restriction by positioning of the armature becomesdetermining, but is positively so only at peak flux when the iron issaturated. Therefore, at instantaneous flux levels below peak, thedivision of primary flux is not necessarily determined by the relativeareas of working contact between the armature and the secondary legs.

This non-linear action produces two undesirable characteristics. .First,the output wave form is very distorted. Second, the voltage regulationor ability to maintain a substantially constant output voltage over arange of electrical loading, is poor. This is because at lowerinstantaneous flux levels there is a permeable path comprising thearmature and both secondary legs, with the secondary coils in additive,series connection. This path has considerable inductance impedance,which varies with the instantaneous value of the flux, being high at lowflux values and relatively loW at peak flux values.

Thus, while such a transformer construction has very importantadvantages, it is characterized by a poor output wave form and pooroutput regulation.

The primary object of my invention is to provide a variable voltagetransformer construction which has no moving, current carrying contactsor the like, and which has good output Wave form and good outputregulation.

Another object of my invention is to provide the foregoing in anextremely simple, highly effective, durable and dependable constructionwhich is little more expensive than simple, fixed transformers of likecapacity.

In one aspect thereof, a variable voltage transformer constructed inaccordance with my invention is characterized by the provision of atransformer core having a primary leg and two secondary legs, a primarywinding on the primary leg and a secondary winding on at least one ofthe secondary legs, and an armature having one magnetic portion arrangedfor working contact with the primary leg and one of the secondary legs,thereby to complete one magnetic circuit therethrough, and anothermagnetic portion arranged for working contact with the primary leg andthe other secondary leg, thereby to complete another magnetic circuittherethrough, with one of the armature and core being movable relativeto the other to vary the relative area of working contact between themagnetic armature portions and the primary leg and thereby vary thedivision of primary flux between the secondary legs.

In another aspect thereof, a variablevoltage transformer constructed inaccordance with my invention is characterized by the provision, in atransformer construction of the type described in the immediatelypreceding paragraph, of means automatically operable in response tovariations .in flux density across the primary leg to maintainsubstantially constant flux density thereacross adjacent the armature,whereby division of primary flux is determined by the relative area ofworking contact of the primary leg with the magnetic armature portionsat all instantaneous flux levels.

The foregoing and other objects, advantages and characterizing featuresof a variable voltage transformer constructed in accordance with myinvention will become clearly apparent from the ensuing detaileddescription of certain presently contemplated embodiments thereof,considered in conjunction with the accompanying drawings illustratingthe same, wherein like reference numerals denote like parts throughoutthe various views and wherein:

FIG. 1 is a side elevational view of one form of variable voltagetransformer of my invention, with the front cover of the enclosinghousing removed;

FIG. 2 is a sectional view thereof, taken about on line II-II of FIG. 1;1

FIG. 3 is a generally diagrammatic side elevational view of thetransformer core and armature of F-IG. 1, illustrating the mode ofoperation thereof;

FIG. 4 is an enlarged, fragmentary, diagrammatic plan view of one formof Working end face of the primary leg thereof;

FIG. 5 is a view corersponcling to that of FIG. 4 but showing a modifiedprimary end face;

FIG. 6 is a view corresponding to those of FIGS. 4 and 5, but showinganother primary end face construction; and

FIG. 7 is a view similar to that of FIG. 3 on menlarged scale, showing amodified armature construction, with the primary and secondary windingsomitted for ease of illustration.

Referring now in detail to the accompanying drawings, one form ofvariable voltage transformer constructed in accordance with my inventioncomprises a corepgenerally designated 1, preferably of a laminatedconstruction known in the art. Core 1 is generally E shaped, having acenter primary leg 2, and two outer, secondary legs 3 and 4. Thelam-ina-tions comprising core 1' are secured together, as by rivets orthe like, and are mounted in a [housing 5 as by means of bolts 6 passingthrough core 1 and threaded'ly engaging embossme-nts 7 projecting fromthe rear wall 8 lot the housing. The front of housing 5 normally isclosed by a removable cover 9, and ventilating openings 10 are providedthrough rear wall 8 and cover 9.

I A primary winding -12 is placed on primary leg 2, and

has leads 13, 14 adapted for connection to a source of exciting voltage,not shown. A pair of secondary windings I15, '16 are placed on the twoouter secondary legs 3, 4, respectively. Wind-ings 15, 1 6 areoppositely wound and series connected, through a common lead 1'7, tocomprise :a differential secondary winding 15, 16 having leads 18 and 19adapted for connection to the load, also not shown. Openings 1 1,surrounded lay grommets 20 (of insulating material, are provided forpassage of primary and secondary leads .13, 14, 18 and 19 out of housing5.

To vary the net voltage introduced in secondary windings 15, 1 6, meansare provided for adjusting the position of an armature 21 relative tothe core, and it is a particular rteature of my invention that thedivision of primary flux determined, not by the relative area of workingcontact of the armature with the two secondary legs, as in the specificdisclosure of the B ojarski application identilied above, but lay therelative area of working contact of magnetically separated armatureportions with the primary end face,

To this end, armature '21 is provided with a magnetic section comprisingportions '22, 22', of laminated, magnetic material, arranged to completemagnetic circuits between primary leg 2 and secondary legs 3 and 4,respectively, which portions are encircled by a body 37 of electricallyconductive material tor a purpose to be described. Armature 21 isconfined for reciprocation in the direction of arrows 23, as by guideshoulders 24 depending from opposite sides of the armature and bearingagainst the primary and secondary legs 3, 4 on opposite sides thereof,thereby confining the armature tor reciprocation in a lengthwisedirection in the plane of the core legs. For moving armature 21, Iprovide a rack 26 projecting from the armature and secured thereto inany desired manner. Rack 26 meshes with a pinion 29 mounted on a shaft30 journa'lled in a :boss '32 carried on the rear wall 8 of housing 5.Shatt 30 extends through the housing wall tor manipulation by a controlknob 33. A boss 35 depends tirom top wall 25 of housing and bearsagainst rack 26 to hold it in meshing engagement'with pinion .29. Aspring 36 is carried by top wall 25 and bears against the upper surfaceof armature 21 to hold the magnetic armature portions 22, 22' in workingcontact with the end faces of the core legs 2, 3 and 4.

Referring now to'rthe schematic diagram of FIG. 3, the neutral positionof armature 21 is shown in lull lines. It will be noted that whenarmature 21 is in its neutral position, the laminated, magnetic portion22 thereof is in working contact with the entire end face area ofsecondary leg 3, and with one-half of the end lace area of primary leg2, while magnetic portion 22' is in working contact with the entire endface area of secondary leg 4 and with one-half the end face area ofprimary leg *2. Therefore, all other raotors being equal, the reluctanceof each magnetic circuit is the same, the p nrnary flux is equallydivided between secondary legs 3 and 4, and because the secondarywindings v15, 16 are opposed to each other the voltages induced thereincancel out, producing a zero output voltage. a

When armature 21 is moved to w e extreme left hand position illustratedin phantom in FIG. 3, its magnetic portion 22' is in working contactwith the entire end face of primary leg 2 as well as of secondary leg 4,and the magnetic section '22 is out of working contact with the end tacoof primary leg 2. Accordingly, the entire primary flux is diverted fromsecondary leg 3 to secondary leg 4, whereby there is produced a netmaximum voltage of one polarity.

Conversely, when armature 21 is moved to its extreme right hand positionshown in phantom in FIG. 3, magnetic portion '22 is in working contactwith the entire end face area of primary leg 2, and magnetic portion 22is entirely out of working contact therewith Accordingly, the primaryflux is diverted to secondary leg 3 to produce,

4 in the chosen example, an equal maximum net voltage of oppositepolarity. Obviously, armature 21 can be moved to any position betweenthe illustrated extremes to produce a net output voltage continuouslyvariable between no voltage and a maximum of either polarity.

Thus, not only can the output voltage :be readily and continuouslyvaried by infinitesimal increments iirom one extreme to the other, butthe two extremes can encompass a reversal of polarity. The primaryreluctance is not effected by such variations in output. rimary leg 2preferably has l2]. cross sectional area equal to that of secondary leg3 and also that of secondary leg 4, all other things being equal, tormaximum utilization of transformer capacity. The primary leg end face isin working contact with one or the other or 'both of the magneticarmature portions 22, 22' at all positions of the armature, wherebythere is no variation in the primary reluctance which is independent ofarmature position.

Thus, it is seen that the instant invention varies the output voltage byvarying the relative area of working contact between the primary leg endface and the mag netic armature portions 22 and .22. However, thediversion of primary [flux to the respective secondaries in proportionto such relative area of working contact of the primary end face withthe magnetic armature portions normally would be so determined only atmoments of peak flux, when the primary iron is saturated and the primaryleg has uni-form flux density thereaoross. At moments of less than peakflux, such division by relative area of working contact would not talceplace a s desired because the iron is not saturated, permitting arestricted primary end face area to pass more flux than is the case atsaturation, and thereby permitting the division of primary flux otherthan as determined by the relative areas of working contact.

It is a particular feature of my invention that it provides meansenforcing substantially equal or uniform density at all points acrossthe end face of primary leg 2, at all instantaneous flux levels, wherebydivision of primary flux is determined at alltimes by relative areas ofworking contact and is not dependent upon saturation. To illustrate howthis is accomplished in my invention, reference is had to FIG. 4 showingthe end face of primary leg 2 divided by a slot 40 into two equal parts41 and 42. A closed winding 43 of highly electrically conductivematerial is placed in slot 40 and around the parts 41, 42 in a figureeight pattern with the winding crossing itself in slot 40. This providesa loop 44 around the primary end face portion 41 and a loop 45 aroundthe primary end face portion 42, with current in loop 44 flowing aroundthe associated primary portion 41 in a direction opposite to the flow ofcurrent through loop 45 around the primary portion 42. An alternatingflux in the primary portion 41 will produce a voltage in loop 44 ofwinding 43, and this voltage will cause a current flow in win-ding 43and through loop 45 in a direction to induce, in primary portion 42, aflux equal to that in primary portion 41 and proceeding in the samedirection. Looking at this another way, if the flux present in portion41 differs from the flux present in portion 42, a voltage will beproduced in one of the loops 44, 45 causing a current to fiow in theWinding in a direction forcing equalization of the flux in the twoprimary portions 41, 42. Only when the flux densities in the portions41, 42 are equal, is there no flux producing current; and if theconductivity of the winding 43 is high enough no substantial differencein flux density can exist between the portions 41, 42.

To demonstrate this, if B and B are the flux in portions 41 and 42,respectively, the voltage V induced in winding 43 is given by theequation d w ds-Bl.)

and the condition enforced by high'conductivity of winding 43 is that Vmust be substantially zero, whereby B =B at every instant if the fluxesare alternating.

In FIG. 4, although portions 41 and 42 must have equal or substantiallyequal flux, it will be seen that the flux can be unequally distributedin either portion 41, 42. Accordingly, a finer sub-division of theprimary leg usually is required, and this can be accomplished in atleast two different ways.

One way of dividing the primary leg is illustrated in FIG. 5, whichshows the end face of primary leg 2 divided into five equal parts 46,47, 48, 49 and 50 by four slots 40. A figure eight winding 51, similarto winding 43, is placed around parts 46 and 47, another figure eightwinding 52 is placed around parts 47 and 48, a similar winding 53 isplaced around parts 48 and 49, and a like winding 54 is placed aroundparts 49 and 50. The windings cross upon themselves in slots 40, asbefore.

From the foregoing analysis it is seen that equality in flux density isenforced as between parts 46 and 47 by winding 51. The same is true asbetween parts 47 and 48, 48 and 49, and 49 and 50. Accordingly, the fluxdensity must be the same in all parts. Obviously, the primary end facecan be divided into a greater or lesser number of blocks or parts.

Another method of accomplishing the desire-d result is by successivesubdivision, as illustrated in FIG. 6. Here, it is seen that theportions 41 and 42 of FIG. 4 are each centrally divided, by slots 55,into parts 56, 57, 58 and 59. A figure eight winding 60 is placed aroundthe parts 56 and 57, crossing itself in the slot 55 therebetween, andanother figure eight winding 61 is placed around the parts 58 and 59,crossing itself in like manner. The winding 43 remains in place aroundthe major division, as described with reference to FIG. 4.

From this, it is seen that winding 43 forces the total flux in parts 56and 57 to be the same as in parts 58 and 59, with the winding 60 forcingthe flux to be the same in parts 56 and 57, and winding 61 forcing theflux to be the same in parts 58 and 59. As a result, the flux density isthe same in parts 56, 57, 58 and 59.

Either system of division and placement of windings can be used,depending upon the specific problem involved, and they may be usedsimutaneously or in an overlapping manner.

Referring again to FIG. 3, it will be seen that the primary end face isbroken up into six equal parts, by five slots with each pair of adjacentparts being linked by a figure eight winding as described with referenceto FIG. 5 As a result, each tooth or part has substantially the sameflux density as each of the other parts, at any instant, whereby theprimary flux is uniformly distributed across the end face of primary leg2 at all times. The division or diversion of primary flux is determinedby the relative areas of working contact between the magnetic armatureportions 22, 22', and the end face of primary leg 2, at all times. Thisavoids the output wave distortion which otherwise would result becauseuniform distribution of flux is not enforced by saturation of theprimary iron other than at peak flux levels.

The problems of secondary reactance and poor regulation are eliminatedin the following manner. Normally, at lower instantaneous flux levels anaiding series circuit comprising armature 21, secondary legs 3 and 4,and core portion 63 could be traced. However, with the armatureconstruction of'my invention if flux from secondary 3 attempts to crossthrough armature 21 to secondary 4, it strikes the separation providedby the notch 27 between the magnetic armature portions 22, 22. Thiswould divert such flux into primary leg 2, and if such flux attempted toreenter the armature, through the magnetic portion 22, it would beblocked by the figure eight windings around the primary end faceportions. This is perhaps best understood by reference to FIG. 4,showing that if flux passed from armature portion 22 into primaryportion 41, and then attempted to enter armature portion 22' through theprimary end face portion 42, the passage of such flux through the loop44 would produce a blocking current in loop 45 preventin the escape ofsuch flux from the primary leg.

The notch 27 in armature 21 has its sides extending at approximately 45from center, the optimum angle being determined by the ability of thenotch formation to channel flux from the primary end face, broken as itis by the slots therein, without reaching saturation in the armatureiron. To block flux attempting to cross notch 27 through air fromportion 22 to portion 22', notch 27 can be filled with highlyelectrically conductive material 28, such as copper. Any passage of fluxinto such material will induce a blocking current, preventing thetransmission of flux therethrough.

A small connecting piece of armature iron may be left at the bottom ofnotch 27, joining the portions 22, 22 to give smoothness to the slidingor working surface of the armature 21. Alternately, the portions 22, 22may actually be separated by a small gap, With the two portions heldtogether by a frame which can conveniently comprise the part 37. Thisframe consists of side pieces 38 and end pieces 39, all of electricallyconductive material which, like conductive material 28, function toblock air leakage of flux in a manner more fully set forth in my pendingapplication Serial No. 112,477, filed May 24, 1961. The notch material28 and end material 39 can be soldered or otherwise electricallyconnected to the sides 38, and the electrically conductive frame can belocked to the laminated magnetic portions 22, 22' as by rivets 65. Thisprovides a mechanically unitary structure for the armature, and blocksunwanted air leakage of flux. Also, as pointed out in my pendingapplication, the guides 24 can be extensions of the sides 38 of thisblocking frame 37.

Instead of the notch 27, the armature portions 22, 22' can be a unitarymember, as shown in FIG. 7, magnetically separated by a short circuitedwinding 67 of highly electrically conductive material received in a slot66 in the bottom face of the armature. Winding 67 encircles the armatureadjacent the juncture between the portions 22, 22', and need not beturns of wire as shown but can be a single piece of copper or otherelectrically conductive wire or ribbon short circuited to itself. Ineither event, any flux attempting to pass from one magnetic armatureportion to the other will set up a blocking current in the winding 67,preventing such magnetic linking of the armature portions 22, 22'.Blocking frame 37 can be applied to this armature, as well, and sides 38can comprise part of winding 67.

Accordingly, it is seen that my invention fully accomplishes itsintended objects, and provides a variable voltage transformer useful fora wide variety of purposes, and having good wave form and goodregulation. Where reversal of polarity is not desired, the transformercan be connected as an autotransformer, using the primary as a base bytapping the primary windings into the secondary windings. Also, otherwinding arrangements could be used. For example, the secondary windingscould be unequal, and additive. Also, an additional secondary windingcan be placed on the same leg as the primary winding, and connected inseries with the other secondaries.

While I have disclosed and described in detail only certain illustrativeembodiments of my invention, it will be appreciated that this has beendone by way of illustration only, without thought of limitation.Variations and modifications such as will occur to those skilled in theart, are intended to be included within the scope of the appendedclaims.

Having fully disclosed and completely described my invention, togetherwith its mode of operation, what I claim as new is:

1. A variable voltage transformer comprising a transformer core having aprimary leg and a pair of secondary legs, a primary winding on saidprimary leg and a secondary winding on at least one of said secondarylegs, an armature having one magnetic portion arranged for workingcontact with an end face of said primary leg and an end face of one ofsaid secondary legs and another magnetic portion arranged for workingcontact with said end face of said primary leg and an end face of theother of said secondary legs, said armature and said core being movableone relative to the other thereof to vary the relative area of saidprimary leg end face in working contact with said magnetic armatureportions and thereby divert primary flux from one of said secondary legsto the other thereof, said end face of said primary leg being dividedinto multiple parts, and short-circuited windings of electricallyconductive material linking pairs of adjacent parts in the manner of afigure eight whereby one part of each pair thereof is encircled by acurrent carrying loop in one direction and the other part of each pairthereof is encircled by a current carrying loop in the oppositedirection.

2. A variable voltage transformer as set forth in claim 1, wherein saidarmature is divided into said magnetic portions by means comprising anotch between said portions substantially separating the same.

3. A variable voltage transformer as set forth in claim 2, wherein saidnotch is substantially filled with electrically conductive materialthereby to block the air leakage of flux across said notch.

4. A variable voltage transformer as set forth in claim 3, together witha body of electrically conductive material encircling the opposite sidesand ends of said armature thereby to block the air leakage of flux fromsaid magnetic armature portions.

5. A variable voltage transformer as set forth in claim 2, wherein saidarmature portions are spaced apart.

6. A variable voltage transformer as set forth in claim 2, wherein saidmagnetic portions are adjacent the armature face arranged for workingcontact with said primary leg.

7. A variable voltage transformer comprising a transformer core having aprimary leg and a pair of secondary legs, a primary winding on saidprimary leg and a secondary winding on at least one of said secondarylegs, an armature, and means dividing said armature into one magneticportion arranged for working contact with said primary leg and one ofsaid secondary legs and another magnetic portion substantiallymagnetically separated from said one portion and arranged for workingcontact with said primary leg and the other of said secondary legs, saidarmature being movable to vary the relative area of working contactbetween said primary leg and said magnetic portions and thereby divertprimary flux from said one secondary leg to said other secondary leg,wherein said armature portions are mechanically joined and wherein saidmeans dividing said armature into said magnetic portions comprise ashort circuited loop of electrically conductive material encircling saidarmature between said portions.

8. A variable voltage transformer comprising a transformer core having aprimary leg and a pair of secondary legs, a primary winding on saidprimary leg and a secondary winding on at least one of said secondarylegs, an armature, and means dividing said armature into one magneticportion arranged for working contact with said primary leg and one ofsaid secondary legs and another magnetic portion substantiallymagnetically separated from said one portion and arranged for workingcontact with said primary leg and the other of said secondary legs, saidarmature being movable to vary the relative area of working contactbetween said primary leg and said magnetic portions and thereby divertprimary flux from said one secondary leg to said other secondary leg,wherein said armature portions are mechanically joined and wherein saidmeans dividing said armature into said magnetic portions comprise ashort circuited loop of electrically conductive material encircling saidarmature between said portions and wherein the face of said arma- 8 turearranged for working contact with said primary leg is slotted to receivesaid loop.

9. A variable voltage transformer comprising a transformer core having aprimary leg and a pair of secondary legs, a primary winding on saidprimary leg and a secondary winding on at least one of said secondarylegs, an armature having one magnetic portion arranged for workingcontact with said primary leg and one of said secondary legs and anothermagnetic portion arranged for working contact with said primary leg andthe other of said secondary legs, said armature portions beingmagnetically substantially separated, said armature and said core beingmovable one relative to the other thereof to vary the relative area ofworking contact between said primary leg and said magnetic armatureportions and thereby divert primary flux from one of said secondary legsto the other thereof, and means automatically operable in response tovariations in flux density across said primary leg to maintainsubstantially equal flux density thereacross adjacent said armature atall instantaneous flux levels, wherein said last-named means comprisemeans dividing the cross-sectional area of said primary leg adjacentsaid armature into multiple parts, and flux equalizing windingsencircling and thereby linking adjacent ones of said parts.

10. A variable voltage transformer comprising a transformer core havinga primary leg and a pair of secondary legs, a primary winding on saidprimary leg and a secondary winding on at least one of said secondarylegs, an armature having one magnetic portion arranged for workingcontact with said primary leg and one of said secondary legs and anothermagnetic portion arranged for working contact with said primary leg andthe other of said secondary legs, said armature portions being magnetically substantially separated, said armature and said core beingmovable one relative to the other thereof to vary the relative area ofworking contact between said primary leg and said magnetic armatureportions and thereby divert primary flux from one of said secondary legsto the other thereof, and means automatically operable in response tovariations in flux density across said primary leg to maintainsubstantially equal flux density there across adjacent said armature atall instantaneous flux levels, wherein said last-named means comprisemeans separating the cross-sectional area of said primary leg adjacentsaid armature into multiple parts, and shortcircuited windings ofelectrically conductive material encircling pairs of adjacent parts witheach winding providing current conducting loops encircling theassociated pair of parts in opposite directions.

lll. A variable voltage transformer comprising a transformer core havinga primary leg and two secondary legs, a primary winding on said primaryleg and a secondary winding on at least one of said secondary legs, anarmature having one magnetic portion arranged for working contact withan end face of said primary leg and an end face of one of said secondarylegs, said armature having another magnetic portion arranged for workingcontact with said end face of said primary leg and an end face of theother of said secondary legs, said armature being movable relative tosaid core to vary the relative area of said primary leg end face inworking contact with said magnetic armature portions and thereby divertprimary flux from one of said secondary legs to the other thereof, saidprimary leg end face being divided into multiple parts of substantiallyequal cross section, and flux equalizing windings of electricallyconductive material encirling said parts in a manner automaticallytending to maintain equal fiuX density in all of said parts.

12. A variable voltage transformer as set forth in claim 11, whereineach of said windings is short-circuited and crossed over upon itself toprovide a pair of oppositely directed current carrying loops encirclinga pair of parts.

13. A variable voltage transformer as set forth in claim 12, whereinsaid primary leg end face is divided into at least three parts, and saidwindings encircle each pair of adjacent parts.

14. A variable voltage transformer as set forth in claim 12, whereinsaid primary leg end face is divided into at least two main parts eachfurther divided into at least two minor parts, said pair of main partsbeing encircled by one of said windings, and each pair of said minorparts being encircled by another of said windings.

15. In a transformer having a flux producing core section, meansautomatically operable in response to variations in flux density acrosssaid section to maintain substantially equal fillX density thereacrossat all instantaneous flux levels, said means comprising, means dividing10 multiple parts of substantially equal cross-section area, and fluxequalizing widings encircling said parts in a manner tending to maintainsubstantially equal flux densities therein.

References Cited by the Examiner UNITED STATES PATENTS 2,253,705 8/41Hedding et al 336-134 X 2,430,757 11/47 Conrad et al 177351 2,495,1571/50 Browne 336-87 2,564,484 8/51 Kuehni 33630 X 2,662,301 12/53 Beach33-226 2,912,767 11/59 Mittelmann 336135 X the cross sectional area ofsaid flux producing section into 15 JOHN F. BURNS, Primary Examiner.

15. IN A TRANSFORMER HAVING A FLUX PRODUCING CORE SECTION, MEANSAUTOMATICALLY OPERABLE IN RESPONSE TO VARIATIONS IN FLUX DENSITY ACROSSSAID SECTION TO MAINTAIN SUBSTANTIALLY EQUAL FLUX DENSITY THEREACROSS ATALL INSTANTANEOUS FLUX LEVELS, SAID MEANS COMPRISING, MEANS DIVIDING THECROSS SECTIONAL AREA OF SAID FLUX PRODUCING SECTION INTO